Supplemental Oil and Gas Disclosures (Results of Ops) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Results Of Operations For Oil And Gas Producing Activities By Geographic Area [Line Items]
Revenues	$ 97,615	$ 83,275	$ 23,003	$ 15,166	$ 16,632	$ 10,302	$ 19,053	$ 14,104	$ 219,058	$ 60,091	$ 71,675
Production expenses	59,857	64,174	41,359	33,867	50,800	42,524	18,304	16,077	58,536	17,668	15,347
DD&A									64,387	25,025	27,293
Impairment of oil and gas properties	6,000	11,400	20,000	15,700	36,900	28,800	0	0	53,072	65,706	7,692
Income tax expense (benefit)									41,748	(12,391)	11,580
Results of activities									1,315	(35,917)	9,763
[GB]
Results Of Operations For Oil And Gas Producing Activities By Geographic Area [Line Items]
Revenues									207,181	41,754	60,501
Production expenses									51,568	8,622	11,086
DD&A									56,813	14,312	22,020
Impairment of oil and gas properties									0	0	0
Income tax expense (benefit)									61,256	11,104	13,698
Results of activities									37,544	7,716	13,697
[DomesticCountryMember]
Results Of Operations For Oil And Gas Producing Activities By Geographic Area [Line Items]
Revenues									11,877	18,337	11,174
Production expenses									6,968	9,046	4,261
DD&A									7,574	10,713	5,273
Impairment of oil and gas properties									53,072	65,706	7,692
Income tax expense (benefit)									(19,508)	(23,495)	(2,118)
Results of activities									$ (36,229)	$ (43,633)	$ (3,934)